The present invention relates generally to high frequency generators and more specifically to a self-starting high-frequency generator, in which in the anode circuit of a grid-controlled electron tube there are arranged an oscillating circuit tuned to the operating frequency and a further oscillating circuit tuned to three times the operating frequency and where a feedback circuit is provided for the feedback of power from the anode circuit to the control grid.
Electronic circuits in the form of self-starting high-frequency generators have long been known in the art ("Taschenbuch der Hochfrequenztechnik", Authors: Meinke & Gundlach, Springer-Verlag, 1956, pages 955 to 957/1992, page M76/77). The feedback of power from the anode circuit to the control grid can take place in different ways, for example by means of the so-called Mei.beta.ner circuit which consists of a frequency-independent transformer feedback in combination with an oscillating circuit arranged in the anode circuit or also by means of a push-pull circuit with capacitive voltage division. In the development of such electronic circuits it is desired, among other things, to achieve the conversion of DC power into AC power associated with these circuits as efficiently as possible. Previously this has been achieved in practice with a so-called class-C-operation (small current-flow angle) and with the realization of a sinusoidal alternating-voltage characteristic, which is as uncorrupted as much as possible, at the anode and the controlled electrode of the grid-controlled tube used.
To improve the efficiency of high-frequency generators it has already been suggested that one or more additional oscillating circuits be arranged in the anode circuit, which oscillating circuits are tuned to the third harmonic or to the third and the fifth harmonic of the fundamental frequency, and that the feedback of power from the anode circuit to the control grid be undertaken with the aid of an amplifier or by means of a diode and additional countervoltage source in such a way that the grid is controlled with an approximate square-wave voltage (DE 404 179; "Elektronik", 1956, pages 136 to 138).
Moreover, in the field of amplifier technology, in particular with radio transmitters, it is known in itself to increase the efficiency of the amplifier operation by the specific addition of the third harmonic to the fundamental wave. This so-called 3-H-operation or D-operation is repeatedly described in the relevant literature (among other things BBC-Mitteilungen 7-80, pages 444 to 448, DE 595 408).
The present invention is directed to the problem of reducing the expenditure in terms of circuit engineering for the feedback of power from the anode circuit to the control grid in a circuit of a high frequency generator of the type discussed above.